The animal core will provide program project investigators with access to aged rhesus macaques and support services for the projects of Drs. Morrison, Kordower and Rapp. A colony of forty aged female rhesus and thirty young control females will be maintained at the California National Primate Research Center for behavioral and neuroanatomical studies. Each animal's database will include daily determination of menses cycle activity, monitoring of reproductive hormone metabolites in the urine, serum hormone levels, and routine clinical parameters such as weights and complete blood counts. The animal core will perform bilateral ovariectomies on aged females and young controls, and chronic or acute hormone replacement with either estradiol and/or progesterone. The animal core will also provide animal handling and transport for behavioral studies. Macaque reproductive and physiological parameters will be easily accessible to all investigators for experimental analysis. The animal core will also provide complete necropsies on all animals. A tissue archive will be maintained and tissues will be distributed to other investigators interested in analyzing specific tissues with regard to aging and estrogen effects.